IMU Data Processing System

This project implements a publisher-subscriber system for IMU (Inertial Measurement Unit) data using Unix domain sockets. It includes AHRS (Attitude and Heading Reference System) algorithms for orientation estimation.

Overview

The system consists of two main components:

1. Publisher: Generates IMU data (either random or from a file) and publishes it to subscribers.
2. Subscriber: Receives IMU data from the publisher, processes it with AHRS algorithms, and displays the results.

Features

• Unix domain socket communication between publisher and subscriber
• Multiple subscriber support
• Configurable data generation frequency
• Timeout handling for detecting disconnected publishers
• AHRS algorithms for orientation estimation
• Clean object-oriented design with factory pattern for AHRS creation
• Real-time execution support (experimental)

Architecture

The system is built with a modular, object-oriented design following these key principles:

• Separation of Concerns: Each component has a specific responsibility
• Dependency Injection: Components depend on abstractions, not concrete implementations
• Interface-Based Design: Abstractions define contracts that implementations must fulfill

Communication

The system uses Unix domain datagram sockets for communication. The publisher creates a socket and listens for registration messages from subscribers. Once a subscriber registers, the publisher sends IMU data to all registered subscribers.

Key Components

1. IMUSocketHandler: Base class providing common socket functionality
2. IMUPublisher: Publishes IMU data to registered subscribers
3. IMUSubscriber: Receives IMU data from the publisher
4. IMUDataProvider: Interface for obtaining IMU data
5. RandomIMUDataProvider: Implementation that generates random IMU data
6. AHRS: Abstract base class for orientation estimation algorithms
7. AHRSFactory: Factory for creating AHRS instances based on user selection

Building

mkdir build
cd build
cmake ..
make

Usage

Publisher

./publisher --socket-path /tmp/imu_socket --frequency-hz 100 --log-level INFO [--real-time] [--priority 80] [--policy FIFO]

Options:

• --socket-path: Path to the Unix domain socket
• --frequency-hz: Data generation frequency in Hz
• --log-level: Logging level (TRACE, DEBUG, INFO, WARN, ERROR)
• --real-time: Enable real-time thread configuration
• --priority: Thread priority (1-99, only with --real-time)
• --policy: Scheduling policy (FIFO or RR, only with --real-time)

Subscriber

./subscriber --socket-path /tmp/imu_socket --log-level INFO --timeout-ms 5000 --ahrs-type madgwick [--real-time] [--priority 75] [--policy FIFO]

Options:

• --socket-path: Path to the Unix domain socket (must match publisher)
• --log-level: Logging level (TRACE, DEBUG, INFO, WARN, ERROR)
• --timeout-ms: Timeout in milliseconds for detecting disconnected publisher
• --ahrs-type: AHRS algorithm to use (none, madgwick, simple)
• --real-time: Enable real-time thread configuration
• --priority: Thread priority (1-99, only with --real-time)
• --policy: Scheduling policy (FIFO or RR, only with --real-time)

Real-Time Execution Support (Experimental)

⚠️ IMPORTANT: The real-time features have not been tested in a real-time environment. Use at your own risk.

The system includes experimental support for real-time execution with the following features:

• Real-time thread scheduling (SCHED_FIFO or SCHED_RR)
• Configurable thread priorities (1-99)
• Memory locking to prevent paging
• Priority inheritance for mutexes
• Separate priority levels for publisher and subscriber

Real-Time Requirements

To use real-time features:

1. System Requirements:

   • Real-time kernel (PREEMPT_RT patch or similar)
   • Appropriate user permissions for real-time scheduling

2. System Configuration:

   # Add to /etc/security/limits.conf:
   your_username    hard    rtprio    99
   your_username    soft    rtprio    99

3. Recommended Practices:

   • Disable CPU frequency scaling
   • Disable power management features
   • Consider CPU isolation using kernel boot parameters
   • Configure network interfaces with appropriate priorities

Real-Time Usage Example

# Publisher with real-time enabled
sudo ./publisher --socket-path /tmp/imu_socket --frequency-hz 100 --real-time --priority 80 --policy FIFO

# Subscriber with real-time enabled
sudo ./subscriber --socket-path /tmp/imu_socket --timeout-ms 5000 --ahrs-type madgwick --real-time --priority 75 --policy FIFO

Design Patterns

The project uses several design patterns:

1. Factory Pattern: The AHRSFactory creates appropriate AHRS instances based on user selection.
2. Strategy Pattern: Different AHRS algorithms implement the same interface, allowing them to be used interchangeably.
3. Observer Pattern: The publisher-subscriber model follows the observer pattern.
4. Template Method Pattern: Base classes define the skeleton of operations, with specific steps implemented by derived classes.

Modern C++ Features

The project demonstrates several modern C++17 features:

1. std::optional and std::variant: Demonstrated as an alternative to inheritance-based polymorphism in the VariantAHRS class.

Thread Safety

• The publisher uses mutex protection for the subscriber list
• The subscriber implements timeout detection for publisher failures
• Both components handle graceful termination with proper resource cleanup

Resource Management

• Automatic cleanup of socket resources in destructors
• Detection and removal of disconnected subscribers
• Proper signal handling for graceful shutdown

Dependencies

• C++17 compatible compiler
• CMake 3.10 or higher
• spdlog for logging
• pthread for threading